The vehicle control systems for automotives have increased significantly recently. They include the following vehicle dynamics control or active safety systems such as ESC (yaw stability control), RSC (roll stability control), ACC (adaptive cruise control), HD/A/HC (hill decent/ascent/hold control), ABS (anti-lock brake system), EBD (electronic brake distribution), TCS (traction control system), suspension control systems, steering controls, drive-train controls, engine controls, etc. Many of these systems activate available actuators in response to the sensed vehicle and drive conditions so as to augment the driver's driving capability and to improve the driving comfort and to prevent accidents from happening.
Both OEMs (original equipment manufacturers) and the auto suppliers are involved in the development and implementation of such vehicle dynamics control systems. The OEMs mainly focus on system level performance and on how to interact with or supervise various systems supplied by the auto suppliers. The OEMs may need a vehicle system level ECU (electronic control unit) separate from the suppliers' ECUs to conduct such an interaction and supervision. Hence it is the OEM's job to coordinate different functions residing in different ECUs so as to guarantee that all the suppliers' ECUs work seamlessly together to achieve favorable vehicle system level performance. The auto suppliers mainly focus on developing individual control functions residing on their corresponding ECUs.
With current advances in mechatronics, the afore-mentioned control systems are being designed to achieve unprecedented performance, which before were only deemed suitable for spacecraft and aircraft. For example, the gyro sensors widely used in aircraft have now been used for achieving better and new control functions; the anti-lock brake system once invented for airplanes has now become a standard commodity for automotives and its capability is still unlocking due to the better discrimination of the vehicle operating states. The current cost reduction trend in hardware technology is opening room for the addition of more sensors and more actuators to be used in developing new functions and in achieving better vehicle dynamics and safety controls. Although auto suppliers are playing important roles here, occasionally, OEMs may also be involved in this area.
Besides the aforementioned ECU integration and development of new functions, function integration is receiving more and more attention. A function integration is also important due to the increasing usage of multiple actuators and the fact that many of the actuators can affect multiple control functions. That is, there are operational overlaps such that multiple actuators could affect the same type of control functions specified for certain vehicle dynamics (for example, both ESC and RSC can alter the vehicle oversteer). It is desirable to coordinate the different control functions so as to achieve the optimized system level performance and eliminate potential performance conflicting operations. One of the key enablers for coordinating multiple control functions is that the vehicle dynamics conditions used in individual control functions are determined based on the sensors in an integration sense. This can apparently be achieved if all the sensors used in measuring the various vehicle system states are all utilized simultaneously and certain new types of motion sensors are introduced for further vehicle dynamics discrimination. Such a sensing technology is called an Integrated Sensing System in this invention. Typical vehicle dynamics states required by multiple vehicle control systems include the variables characterizing the three-dimensional motions of a vehicle and the variables characterizing the control functions controlling such three-dimensional vehicle dynamics.
In an ESC and a RSC system, the control task involves three-dimensional motions along the vehicle roll and yaw angular directions, and its longitudinal and lateral directions. The coupling between different motion directions in those two systems may not be as strong as in an aircraft or a spacecraft. However they cannot be neglected in real time determination of vehicle operation states and in most of the maneuvers. For example, the excessive steering of a vehicle will lead to an excessive yaw and lateral motion, which further introduces large roll motion of the vehicle body towards the outside of the turn. If a driver brakes the vehicle during the excessive steering, the vehicle body will also have pitch and deceleration motions in addition to the roll, yaw and lateral motions. Hence, a successful control system must involve an accurate determination of the vehicle body attitudes due to the dynamic maneuvers. Such attitudes are of a relative feature, that is, they start to be computed when aggressive steering starts. The attitudes are called relative attitudes.
Notice that there are two types of relative attitudes. One is solely due to the suspension motion, which is a good indication of the relative displacement between the vehicle body and the axles of the wheels. Such relative attitudes are called the chassis relative attitudes. The other relative attitudes are due to the angular difference between the vehicle body and the average road surface determined by the four tire-road contact patches. Such relative attitudes are called the vehicle body-to-road relative attitudes. Notice also that when the four wheels are contacting the road, the body-to-road relative attitudes are the same as the chassis relative attitudes. When there is at least one wheel up in the air such as in a rollover event, the magnitudes of the body-to-road relative attitudes are greater than the magnitudes of the chassis relative attitudes.
The vehicle angular motion such as roll, pitch and yaw can be measured through the gyro sensors such as roll rate, pitch rate and yaw rate sensors. However, the measurements of all those angular rates are of an absolute nature, i.e., they are all measured with respect to the sea level. Hence a continuous computation of the vehicle attitudes based on the three angular rate sensors can only provide vehicle attitudes with respect to the sea level. Such vehicle attitudes are called global attitudes.
The vehicle global attitudes may be used to capture the road profiles such as road bank and slope. For example, if a vehicle is driven on a three-dimensional road surface, the difference between the global attitudes calculated from angular rate sensors and the maneuver-induced relative attitudes can be well used to define the road bank and inclination experienced by the vehicle. If the road surface is flat and the vehicle is in a steady state driving condition, then the vehicle global attitudes are the same as the road bank and inclination.
One reason to distinguish the aforementioned relative and global attitudes is that vehicles are usually driven on a three-dimensional road surface of different terrains, not always on a flat road surface. For example, driving on a road surface with a large road bank increases the roll attitude of a vehicle, hence increasing the rollover tendency of the vehicle. That is, a very large global roll attitude may well imply an uncontrollable rollover event regardless of the flat road driving and the three-dimensional road driving. However, driving on a three-dimensional road with moderate road bank angle, the global roll attitude may not be able to provide enough fidelity for determining a rollover event. Vehicular rollover happens when one side of the vehicle is lifted from the road surface with a long duration of time without returning back. If a vehicle is driven on a banked road, the global attitude sensing will pick up certain attitude information even when the vehicle does not experience any wheel lifting (four wheels are always contacting the road surface). Hence a measure of the relative angular displacement of body-to-road relative attitudes provides more fidelity than global roll attitude in detection of a potential rollover event.
Another need for relative attitudes is for yaw stability control. The sideslip angle of the vehicle is a relative yaw angle with respect to the vehicle path. Sideslip angle has a profound impact on vehicle yaw control performance. Since the lateral and longitudinal tire forces are all generated on the planes of the tire-road contact patches, Newton's law must balance the total forces on an average road plane, which is an average indication of the four tire-road contact patches. The frame, which is fixed on the average road surface defined by the four tire contact patches but moves with the vehicle, is called a road frame. Transforming the sensor signals from the sensor frame mounted and fixed on the vehicle body to the road frame requires the knowledge of the relative attitudes between the road frame and the vehicle body frame, and between the vehicle body frame and the sensor frame.
Other than the relative and global attitudes, there is another vehicle body attitude that corresponds to the road unevenness due to potholes and bumps. Such road unevenness induced vehicle body attitudes are of a vibrational nature. That is, they are usually in high frequency and need to be attenuated through either passive or the controlled suspensions. Those attitudes may be called the vehicle vibration attitudes.
Besides the aforementioned vehicle body relative and global attitudes, the vehicle body translation motions are also of significance in achieving vehicle controls. The vehicle's lateral sliding motion usually increases the vehicle dynamically-unstable tendency and makes the vehicle hard to control by ordinary drivers. Hence one of the performance requirements in vehicle dynamics controls is to attenuate the vehicle's lateral sliding motion as much as possible. Notice that such a performance requirement is different from car racing, where vehicle sliding motion is sacrificed for speed. One of the reasons is that the race car drivers are capable and experienced drivers, who can handle the vehicle well even if it is experiencing a large lateral sliding motion. The vehicle's lateral control variable is characterized by its lateral velocity defined along the lateral direction of the vehicle body. Such a velocity cannot be directly measured and it is usually determined from the lateral accelerometer measurement. The output of the lateral accelerometer is also related to the variables other than the lateral velocity, which includes both gravity and centripetal accelerations. On a banked road, gravity contributes to the lateral accelerometer measurement in addition to the vehicle's true lateral sliding acceleration and centripetal acceleration. Due to the fact that the gravity is fixed in both its magnitude and its direction with respect to the sea level, the vehicle global attitudes can be used to find the relative position between the gravity vector and the vehicle body directions. For this reason, the vehicle global attitudes are used to compensate the gravity influence in the measured lateral acceleration such that the vehicle lateral velocity due to pure lateral sliding can be isolated and determined.
The vehicle's longitudinal motion can be controlled by the brake and drivetrain controls. It can be captured through the wheel speed sensors, which measure the rotational rates of the four wheels. When the wheels' rolling radii are known and the wheel or wheels are free rolling, the vehicle longitudinal velocity can be accurately determined through wheel speed sensor signals. During brake actuation or driving torque applying, the wheel or wheels are likely to deviate from the free rolling state. Therefore, the wheel speed sensors alone cannot provide accurate vehicle longitudinal speed information. The gravity-compensated (through the vehicle's global pitch attitude) longitudinal acceleration sensor signals can be used together with the wheel speed sensor to obtain an accurate and robust vehicle longitudinal velocity.
With the aforementioned needs, it is apparent that additional sensor elements to the current sensor set used in current vehicle stability controls may be required.
In an ESC system, a CMS (centralized motion sensor) cluster mounted on a centralized place located within the vehicle body is used. Such a CMS cluster includes a lateral (and/or longitudinal) accelerometer and a yaw rate sensor and ESC uses such a CMS cluster together with certain DS (decentralized sensor) elements at the other locations such as the wheel speed sensors and the steering wheel angle sensor.
The roll stability control system (short to RSC) offered in vehicles from Ford Motor Company, uses a CMS cluster that adds an additional roll rate sensor to the ESC CMS cluster. The roll rate sensor is used in order to discriminate the roll motion of the vehicle body so as to control the potential rollover of a vehicle.
In the current invention, variations of the CMS cluster are used. Such a centralized motion sensor cluster could contain less than six, six, or greater than six inertial sensor elements.
Hence it is desirable to design a centralized integrated sensing system which uses the aforementioned centralized motion sensor cluster, the decentralized sensor group including other discrete sensor units, the actuator specific sensor units, etc., to determine dynamics states including various types of attitudes, the directional velocities, various forces and torques applied to the vehicle, driving conditions such as the road profile and vehicle loadings, etc. Various variables calculated in such centralized integrated sensing system are provided to various individual ECUs and to the system level ECU, or to the different partitions within an ECU in an integration sense for achieving a refined and optimized system level vehicle control performance. Such centralized integrated sensing system could reside within a system level ECU called IVC ECU (integrated vehicle control ECU) or could also reside in one of the supplier's subsystem ECUs.
Besides being used in vehicle dynamics controls, the aforementioned integrated sensing system may be used for active safety and passive safety systems. Many vehicles such as sport utility vehicles and light trucks equipped with the aforementioned vehicle dynamic controls for accident prevention are also equipped with other injury prevention features such as advanced occupant protection systems including various airbag systems and side curtains, crash mitigation system, pre-crash sensing systems, motorized seatbelt pretensioners, dynamic suspension height adjustment systems and the like. Currently, these systems operate as independent features or functions without realizing the synergistic benefits, the system simplification, and cost saving opportunities from an integrated systems approach. It would therefore be desirable to share the sensor units as much as possible and share the sensing algorithms and the computed variables so that cost savings and better system level performance may be achieved.
Due to the complexity of the vehicle control systems, it is sometimes not enough for the OEMs to work only on integrating control functions developed exclusively by auto suppliers. Therefore the aforementioned control function integration is never a simple job, especially when such function integration involves the control function, logic and software developed from both OEMs and auto suppliers. Many times, the control function partition between the OEMs and the auto suppliers are crossed in order for the OEMs to achieve specific vehicle performance requirements deemed important by the OEMs. For instance, the OEMs sometimes develop their own control functions, which may be in subsystem level. Such functions are either the enhancement over the existing control functions or new functions. For example, the RSC control function (including both the algorithms and the production code running in a production ECU environment) were developed by Ford Engineers in-house, and the brake system supplier is responsible for embedding Ford's software into its own brake ECU and interacting with other brake control functions developed by the brake supplier. That is, physically, the new functions developed by the OEMs reside in one of the supplier's ECUs. In this case, the auto supplier has the responsibility to integrate, into its own ECUs, the OEMs' software and its own software while the OEMs take the full responsibility for the overall vehicle system level function integration.
The OEMs could also develop a new subsystem level control function like RSC, which resides in its own system level ECU. In this case, the auto suppliers need to provide certain interfaces such that OEMs' ECU could access to each individual subsystem ECU.
Hence it is also desirable to define the function so as to guarantee that the aforementioned OEM development can be feasibly implemented using the current vehicle control system structure.